Surge control problems have been around as long as the centrifugal compressor itself. Many different approaches have been taken to improve operating range to surge (both in head and flow) depending on what type of surge mechanism is present in the compressor system. Compressor surge triggered by diffuser stall can be suppressed by variable diffuser geometry, whereas surge from impeller stall can be eliminated by the use of variable-geometry inlet guide vanes.
A given compressor duty in terms of flow and pressure ratio can be realized by an infinite number of combinations of inlet guide vane/variable diffuser geometry settings. These various realizations of the same duty point have different compressor efficiencies.
The need exists for an improved method for selecting specific combinations to improve efficiency while maintaining surge-free operation of the compressor, and it is the primary object of the present invention to respond to this need.